University of British Columbia zoology professor Charles Krebs said the oversexed rodents kill each other as feverishly as they breed in a four-year cycle that forms the basis of the Arctic food chain.

"It's like gang warfare run amok. These animals are so aggressive to one another they will kill each other's offspring. They will also kill each other, if they have the opportunity. You have situations where the females will kill the babies next door," Krebs said.

Krebs and co-researcher Don Reid have spent the last five years studying lemmings at a government-financed research station on the Arctic Ocean in Canada's Northwest Territories.

They have monitored the lemmings by putting tiny radio transmitters around their necks both inside and outside a fenced 25-acre enclosure at the Pearce Point research station 600 miles north of Yellowknife.

Krebs, who plans to publish his findings in the Canadian Journal of Zoology, said the popular notion that lemmings hurl themselves off cliffs or drown themselves by wading into the ocean is nonsense.

"That's a Walt Disney myth. There's absolutely no evidence that it has ever happened. It's totally crazy," he said.

Krebs also dismissed the recent theory of Norwegian scientist Arne Semb-Johansson that lemmings commit suicide in a frenzied attempt to escape the stress caused by their colossal sex drive.

"There's no animal that commits suicide, it's a biologically impossible concept. I will pay anybody $1,000 to show you a picture of any two or more lemmings jumping over a cliff. It does not happen," Krebs said.

He said there was even less evidence to support the theory, popular as recently as the 19th Century, that lemmings come from the heavens.

"There are actual descriptions in the 1800s in Scandinavia of people who saw them falling from the sky," he said.

But he confirmed that lemmings are prodigious breeders.

"Individual lemmings can have four or five babies every three weeks. If they put their mind to reproduction, they could fill the world with lemmings," he said.

That is why they need to have a very high death rate, he said. "As the numbers build up, they get more vicious. They basically fight over breeding territory."

Krebs said female lemmings will bite another's litter of three to five babies to death in a matter of seconds. "But so far, we have never had any evidence that they are cannibals. They just seem to kill one other and go away."

He said lemmings, which are bigger than mice and smaller than rats, are important because they provide food for Arctic predators as diverse as owls and grizzlies.

"The ecological system in the Arctic is going up and down because of what these lemmings are doing to each other," he said.

He said it appears the lemming population rises and falls in three- to four-year cycles. "When their numbers get very high, they start killing each other."